1. Field of the Invention
The present invention relates to a reactor for catalytically dewaxing a waxy distillate consisting of a lubricating oil or liquid petroleum feedstocks utilizing a shape-selective crystalline aluminosilicate zeolite catalyst in order to obtain a lubricating oil having a low pour point and a high viscosity index, and more particularly, relates to a novel and unique hydroprocessing trickle reactor construction of the tower-type for catalytically dewaxing liquid petroleum feedstocks.
In the hydroprocessing of liquid petroleum feedstocks, and particularly so called heavy feedstocks, it is a basic purpose of the process of catalytically dewaxing the liquid petroleum feedstocks of removing lighter conversion products from the liquid petroleum flow while concurrently providing a hydrogenative environment for catalytic conversion, which is particularly utilized in the case of the processing of highly waxy feedstocks, such as in catalytic lube processing. Frequently, lighter products which are obtained from cracking and/or hydrocracking reactions compete with the heavier feed molecules for access to the acidic cracking sites in zeolites or silica-alumina cracking catalysts which are employed in the implementation of the catalytic dewaxing processes. In as much as these lighter products diffuse more rapidly into the catalyst than the larger feed molecules, they have a tendency to retard the rate of conversion of the heavier molecules. Moreover, the lighter products also tend to be either more difficult to crack, such as low molecular weight parafins, or easier to polymerize, such as low molecular weight olefins, and possess a tendency to coke more readily then their heavier counterparts so as to thereby retard the conversion of the heavier molecules to an even greater extent.
2. Discussion of the Prior Art
This competition between the light and heavy liquid petroleum molecules obtained from the cracking or hydrocracking process for access to catalytic sites is rendered particularly critical when there is employed a catalyst which is essentially constituted of a shape-selective zeolite, for example, a defined crystalline alminosilicate zeolite catalyst, such as ZSM-5, for the dewaxing of liquid petroleum or lube stocks under moderate hydrogen pressures (400 psig) and at moderate temperatures (550.degree. F. to 675.degree. F.). In a typical reactor employing a zeolite catalyst, such as zeolite ZSM-5 compounds which boil at temperatures higher than 650.degree. F. flow concurrently with naphtha and LPG over the shape-selective catalyst. Processes and reactors which utilize aluminosilicate zeolite catalysts, such as ZSM-5, or other zeolites having smaller pore openings, such as ZSM-11, ZSM-12 and larger then those of erionite or zeolite ZK-5; ZSM-23 and ZSM-35, are disclosed in Bruce P. Pelrine et al. U.S. Pat. No. 4,222,855 and in Nai Y. Chen et al. U.S. Reissue Pat. No. 28,398, both assigned to the Mobil Oil Corporation, and the disclosures of which are incorporated herein by reference. Although the utilization of different types of hydroprocessing reactors for the implementation of catalytic dewaxing processes for liquid petroleum lube or feedstock is broadly disclosed in the prior art, as exemplified by the above-mentioned U.S. patents, broadly referring to stirring tank-type reactors or trickle bed reactors, there is an obvious need in the technology to more precisely define specific hydroprocessing reactor designs which, in a highly efficient and novel manner, will facilitate the removal of the lighter product from the liquid petroleum feedstocks through the intermediary of hydrogen stripping while concurrently preserving an intimate three-phase contacting relationship among hydrogen, liquid petroleum feedstock and catalyst, which is necessary for the efficient hydrotreatment and upgrading through the dewaxing of the liquid petroleum feedstocks.